Congrats, Rob-you got it exactly right!

The Brodie system was the successful brainstorm of Lt. James H. Brodie of the US Army to provide air observation of a convoy by basing one or more systems on convoy ships to help detect enemy submarines from attacking the convoy ships. It was never used this way, however. It was conceived to be used on land also, to deploy liaison aircraft over jungles. It was tested in prototype form in the Gulf of Mexico from a ship successfully by early 1943.

It was successfully used in the Okinawa campaign in the Pacific ocean.

So, what was it? The operational Brodie system consisted of two horizontal booms attached to the ship's hull with short masts on an LST (Landing Ship, Tank) carrying a taut cable 300 feet long suspended 50 feet over the ocean. L4 and L5 liaison aircraft used a "hook" device to suspend the aircraft from the cable. The speed of an LST was only 8 knots, so steaming for aircraft launch or recovery was done into the prevailing wind. "Landing" or retrieving the aircraft to hook onto the Brodie cable was done in the same way. The L4 and L5 pilot and observer had to rappel down to and up from the aircraft

The system worked so well in test practices at Fort Sill, Oklahoma with a 500 foot cable that at least one pilot from 1,000 feet altitude shut down his engine and "dead stick" trapped his aircraft below the Brodie cable in preliminary tests. Tests were also done off San Diego, California over the Pacific ocean. The system was highly secret, developed and tested under the auspices of the US Office of Strategic Services, OSS which was the forerunner of the present CIA-Central Intelligence Agency.

In June of 1944 a Brodie system was installed on LST-776 that participated in the Okinawa invasion and used there successfully. LST-776 Brodie system liaison aircraft flew directed-fire missions for 24 fire missions from 155mm howitzers on Keisa Shima, 8 miles from Okinawa that supported initial successful beach-head landings on Okinawa.

The British liked the Brodie system and tests were done in India on a land-rigged system, but with retreat of Japanese forces from Burma-the usage was dropped.

Incidentally, my late cousin Augie in the US Navy 1941-1945 was a sound-powered talker on the deck of an LST during the invasion of Tarawa Atoll where the Japanese forces were imbedded in reinforced concrete slit trenches and the US forces first used flamethrowers to overcome them and secure the atoll to rebuild a runway on it.

As an aside, I made several trips to Okinawa on Navy business when I worked at the Naval Missile Center in the late 1960s before it reverted to Japan. There was a lot of US military history and bases on Okinawa, Naval aviation, US Marine Corps aviation, USAF aviation and the entire northern end US Army forces when I worked there.

Thanks again for the quick and correct answers.